Close Evaluation of a 1966 National (Valco) Model 70 Bass Amplifier

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In this video, we take a close look at a 1966 National Model 70 Bass Amplifier. Like all National amps, it was actually made by Valco in Chicago, Ill. One of the most attractive amps ever made, the National Model 70 was produced to compete with the Fender Bassman Amp, i.e. initially as a bass amp, but also offering excellent tone and power for guitar use. All features and details are covered as well as suggestions for improvement and an opportunity to hear the three different tones made available by the Guitar, High Bass, and Bass selector switch. If you would like to see similar videos of classic amps and jukeboxes, please see the many other offerings on this site, as well as on our companion channel: Uncle Doug. Thanks !!!

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17 окт 2024

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Комментарии : 33

@UncleDoug 11 лет назад

A couple additional notes re the Model 70: When discussing the 68K resistor in the "Guitar" channel, I neglected to mention that it went to ground, thus providing an 'escape route' for bass frequencies. The increase to 2.2 Meg provided much better tone. The labels are missing from the Jensen Special Design speakers probably due to the heat from the two 6L6's and 5U4 tubes just beneath the magnets....not a great design (they could use heat shields).

@ElPasoTubeAmps 11 лет назад

We're in El Paso, Texas

@benjaminbarnier2996 4 года назад

very cool.

@mixolydian2010 10 лет назад

Beautiful looking and sounding amp. Funny how two of my favourite tube repair guys have hooked up. Neat. Thanks to you David for hosting and Doug for his amp and explanations.

@UncleDoug 9 лет назад

mixolydian2010 You're welcome, Colin, and thanks for your kind words. Glad you enjoyed it :)

@mixolydian2010 9 лет назад

Hi Doug how are things? Its always good to hear from you and your comments about changes or adding components to tone controls always blows me away, you make it sound so simple. Sometimes its hard to pin these things down, your experience and knowledge is always welcome. Thanks. Colin

@UncleDoug 9 лет назад

Things are great, Colin. Rusty and I have been taking a little time off for other hobbies and have been shirking our video duties lately. It's always great to hear from you, too. I tend to rely on trial and error, clipping in or bypassing components, when fine tuning the tone controls. Calculations can get you in the ballpark, but the ear is always the final judge :)

@roncarter2188 2 года назад

Do you where I could source a schematic for this amp? I just bought this exact amplifier in a head version. Thanks for any help.

@ElPasoTubeAmps 2 года назад

I would suggest typing in the make and model of the amplifier in multiple ways and just continue searching for the service manual and schematic and hopefully, you will come up with something. That is the way I do it and almost always find something. Try this and look down the list for Valco. Maybe it will help. megadistortion.com/schematics/

@roncarter2188 2 года назад

@@ElPasoTubeAmps Yes usually I can come up with a schematic after some searching but this one has been a problem for me to try to locate and sometimes I can find a schematic that's close to the original amp, but thank you for the input and I'll keep searching.

@chokkan7 8 лет назад

The grill cloth seems similar to that of a mid-'60s Gibson I have, and it's wonderful...do you know of any current sources for replacement material?

@UncleDoug 8 лет назад

Thanks, C7. No, I have never tried to locate material like this, but would probably check with Antique Electronic Supply, or any old local upholstery supply stores in my area. Good luck.

@UncleDoug 11 лет назад

Thanks CP1 !! We have a companion channel that also features vintage amps and jukeboxes. Just click on my icon to check it out.

@gerrya4897 10 лет назад

Hi, great video! I have a Gretsch amp that i want to add a 3 prong cord to and wanted to know if you have a schematic on how you did the National's with the polarity switch. Thank you

@UncleDoug 9 лет назад

Gerry A Thanks, Gerry. When installing a 3-wire cord, it's best to either bypass the polarity switch, or jumper it so that switching it has no effect. The polarity of the plug ensures that the "hot" input lead is always the correct one, so you don't want the switch to interfere. I'm sorry, but I don't have a schematic.....you'll have to improvise.

@bucyruserie1211 9 лет назад

Hi D&D, what an interesting amplifier, and quite good looking as well (as you mentioned). Really neat with the chrome chassis offset by the black speakers and transformers. I'm a little confused on the operation of the output though. Do all 4 6l6's and the 2 rectifier tubes operate all the time? Or does it switch to one set or the other depending on the selection of Guitar, Hi Bass or Low Bass? If not, why the dual rectifier tubes? I thought the amp sounded great on all the voices. Thanks for another great video!

@UncleDoug 8 лет назад

You're welcome, Tom. All four output tubes work at all times to achieve (or at least approach) the 70W stated output rating. Two rectifier tubes are necessary to fulfill the substantial high voltage current demands of four 6L6GC's.

@roncarter2188 2 года назад

@@UncleDoug Ok then since my amp is in a head version with no speakers, I need to be using both speaker outputs or I'll damage one of the output transformers. Good to know this. Thanks for the info guys.

@roncarter2188 2 года назад

@@UncleDoug Yes my amp is the same amp. Having two output transformers and there are two output speaker jacks, one on each end on the back of the amplifier. Unless maybe they have both outputs wired to one output speaker jack? I'll have to take the chassis out and see what it looks like, since this amp was originally a combo and maybe it was in bad shape or busted up so they made or cut it down to make it into a head. It's sounds very nice so I'll have to see what mods were done if any. Thanks for the input.

@roncarter2188 2 года назад

@@UncleDoug I'm sure someone added these jacks since they don't look original to the chassis. But like the amp demoed, there are two output transformers and that was why I was concerned. about it.

@UncleDoug 2 года назад

@@roncarter2188 I have deleted my previous replies, Ron. Having seen the photos of your cut-down, head version.....which was probably created by someone who wanted to reduce the prodigious weight of the combo unit with two 12" speakers......it is evident that BOTH speaker jacks would have to be connected to speakers. In the original, combo version, one speaker is connected to each OPT, creating a stereo amplification system, but after the cut-down and addition of an output jack for each OPT, you will HAVE to connect a dedicated speaker to each jack or risk damaging the circuit of the amp that has no speaker. The Model 70 is a true stereo amplifier and thus requires two separate speakers......one per channel.

@59seank 11 лет назад

That was fun!

@ENDOalley 10 лет назад

How does this compare to the National guitar amps?

@UncleDoug 9 лет назад

Endo Alley It's much larger and more powerful than any other National guitar amp I have seen or owned, but now that it's been modified, the overall sound/tone is about the same......just much louder :)

@davidallen346 10 лет назад

hi there, can u do amp repairs ?

@UncleDoug 10 лет назад

David performs repairs on tube amplifiers for local individuals, but I generally don't (unless it's on an amp that I sold). If you live far away, the freight both ways can be rather expensive, so you're probably better off finding a repair person in your own vicinity.